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Motor engineering knowledge for marine engineers pdf

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Reeds Vol Motor Engineering Knowledge for Marine Engineers. By: Leslie Series: Reeds Marine Engineering and Technology Series. Volume: Reeds General Engineering Knowledge for Marine Engineers - Free ebook download as PDF File .pdf) or view Volume 05 - Reed's Ship Construction For Marine Students (5th Edition ).pdf Reeds Motor Engineering Knowledge. KNOWLEDGE FOR MARINE soundofheaven.info - Ebook download as PDF File motor counter bear~ng 19 MATERIALS REED'S GENERAL ENGINEERING.


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PDF Download Reeds Vol 12 Motor Engineering Knowledge for Marine Engineers (Reeds Marine Engineering and Technology Series). MOTOR ENGINEERING KNOWLEDGE FOR MARINE ENGINEERS. Revised by Paul A Russell Thomas D Morton Leslie Jackson Anthony S. Read and Download PDF Ebook reeds vol 12 motor engineering knowledge for marine engineers 1st edition at Online Ebook Library. Get reeds vol 12 motor.

Where a pinhole exists sound 'leaks' through and where a tube is thinned it vibrates like a diaphragm transmitting the sound through the tube wall. Abdel Nasser Al-sheikh Yousef. If steel has been cold worked in manufacture the ferrite grains and the pearlite are distorted. Testing of materials tensile, hardness, impact, etc. If after 5 when the glass is full of water, the steam cock is opened and the water in the glass does not descend in the glass, the water level is above the steam cock connexion to the boiler and there is a danger of priming the boiler if any additional feed is put into it. Material required should be hard. Electronic system can easily be set up to obtain such a result even on high-speed engines.

When the operating handle is depressed the shutter uncovers the ports down movement of the handle opens a shutter just below the ports by means of a ratchet. Just before the flashpoint is reached a blue halo occurs around the flame. The value of viscosity index is usually determined from a chart based on a knowledge of the viscosity values at different temperatures. The oxygen supply is to give an internal pressure of 26 bar and should not be less than 24 times the theoretical oxygen required.

The value quoted is the higher calorific value in every case in preference to the lower value. Great care should always be taken regarding the control of heat to heaters situated on the suction side of the fuels pumps so as not to cause oil vaporisation and the possibility of explosive vapour formation. Consider Fig. The thermometer used can be read by means of a lens to 0.

Approximate heat energy values of fuels are: The interior of the bomb must be resistant to condensed acidic vapours from combustion. The lower calorific value is more realistic. In special cases where high viscosity oils are used and high degrees of heating are required to produce atomisation. The higher calorific value includes the heat in water vapour formed from water as the products of combustion are cooled. There are numerous makes of bomb calorimeters but the differences are only slight.

For further close details. Fuels always exhibit a fall of calorific value to some extent during storage. As flashpoint is indicative of the fire and explosion risk. The test as conducted is very closely detailed and only a brief synopsis is outlined here. The water equivalent W. This value is an important consideration for lubricating oils working under low temperature conditions e. A small specimen is fired by electric charge under conditions of pressurised oxygen and the temperature rise of apparatus and coolant is noted.

The above calculation. Correction factors are now applied for acids formed under bomb conditions only. This is the calorific value reference fuel.

Various mixtures are used in the bath. It should be noted that under the bomb's combustion conditions high excess air and pressure sulphuric and nitric acids are formed. The test usually conducted is the Z. Steady heat is applied for about one hour. This test has been used much more in recent times in line with the use of high viscosity fuels in Z. The covers must be a loose fit to allow vapours to escape.

The following test is more suitable for oil: After removal of sample and weighing. The test is a means of determining the residual carbon. The result being expressed as say 1 Q7o Water. The heating and test method are closely controlled. Water vapours are carried over with the distilled gasoline and are condensed in the condenser and measured in the lower part of the receiver. The test is usually repeated a number of times to obtain a uniformity of results.

The mass of the sample placed in the silica crucible must not exceed 0. This sketch is very much simplified. Modern fuels. Ash consists usually of hard abrasive mineral particles such as quartz. H16 has very poor anti knock properties and is taken as lower limit zero. Alternatively the quantities can be expressed in ppm for 1 ml of oil sample usually dissolved in industrial methylated spirits.

This number is the mass. This means that by the time the last gas charge is reached the flame front speeds can reach 2. The test must also be carried out under closely controlled conditions. Paraffin hydrocarbons have the best ignition quality and are thus most suitable. Three other tests however. Normal heptane C. Phenolphthalein can be used as the indicator.

In this case tetraethyl lead T. The oil is often alkaline. In a compression ignition engine. Knocking or pinking are characteristic of some I. These are more complex laboratory tests whose description is difficult to simplify and therefore are not considered further.

Therefore octane number is the percentage by volume of iso-octane in a mixture of iso-octane and normal heptane which has the same knock characteristics as the chosen fuel. Also the time interval between fuel injection and firing. Speed and cetane number can be correlated. Test Iso-octane Ca H16 has very good anti knock properties and is taken as upper limit The ash is then expressed as a mass percentage of the original sample. The test is conducted under fixed conditions on a standard engine which usually has electronic detonation detection.

In view of this these tests namely. As a generalisation the 'heavier' the oil the higher the viscosity and flashpoint and the lower the calorific value. This chemical process liberates about Test Cetane is a paraffin hydrocarbon. These combustibles when supplied with oxygen 0 2 from atmospheric air combust and liberate heat. The lubricating oil sample is mixed with water and heated. There are a number of tests. An alternative method called Diesel index can be used but it is not as reliable as cetane number.

This would indicate extra heating. Density is often indicative of cetane number especially in the middle ranges. Thus cetane number is numerically the percentage by volume of cetane in a mixture of cetane and alpha-methyl-napthalene that matches the chosen fuel in ignition quality. Severe corrosion of crankshafts has been caused by sulphur products from fuel oil mixing with any water in the lubricating oil to form sulphuric acids which are carried round the lubricating oil system..

By condensation of these vapours and separation. It is also important to check the lubricating oil for water contamination. Alpha-methyl-napthalene is of low ignition quality and is taken as the lower limit of zero.

Some success has been achieved by the use of additives such as acetone peroxide. If the carbon is incompletely burned to form carbon monoxide C O and that gas leaves the system unburned the following results. Exothermic reactions are those involving heat evolution.

Analysis of Fuel Oils Typical It is not practice to assume a trend with one variable will apply to another. At high temperatures the very small percentage of the sulphur present as sulphates in the fuel is partly expelled as sulphur trioxide SO3. W el m hcv hydrogen The percentage of SO3 to SO2 during normal combustion is low. The residual oils in regular use today contain. This reaction is of negligible importance from a heating viewpoint but is very important from the viewpoint of corrosion.

This chemical process liberates about 9. The 2. If the steam escapes from the plant uncondensed. Icv hydrogen All the figures given in Table 2.

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A series of common gases and their properties in combustion are given in Table 2. The terms stp and ntp are not rigid in definition and the assumptions made should be clearly stated. The oxygen required for combustion on a theoretical basis can be determined from the combustion equations. This results in the condensation of acid vapours on colder metal surfaces.

In the I. Other hydrocarbons. Chemical reaction: Olo C 0 2 by mass is higher. This is a very relevant problem in air heaters and economisers of boiler plant and cylinder liners of I. Temperature increase tends to increase the range of flammability. In practice complete combustion can only be achieved by supplying excess air.

The presence of SO3 has been shown to raise the acid dewpoint of the gases. Nitrogen takes no part in the combustion process merely representing a large but unavoidable heat loss as being inert it is heated and passes up the uptakes to waste.

Methane is a gas released in bunker spaces.. Sulphurous acid is relatively harmless and unstable and in the presence of free oxygen. All the combustion equations given are based on perfect gases measured at the same temperature and pressure. Standard temperature and pressure stp is usually adopted as a basis in combustion work. CH4 at Dilute acids attack the metal continuously but strong acids cause an initial attack which is then stifled by a passive gas layer or skin developed on the metal surface.

Value varies from Theoretical values are based on cold gas with theoretical cold air supplied. For really elevated boiler conditions Calcium Hydroxide or Zinc Oxide additives can be used: Oxides of Barium.

The sulphate compounds formed have a higher ash melting point and there is little risk of fused deposits. Additives are usually added directly to the empty oil fuel bunker tank before bunkering in quantity about 0.

It is also usual to find an increase in flue gas temperature indicating better furnace or cylinder combustion. Na2S04and FezS04 as the salt water compounds act as a flux as well as providing slag products directly. In the case of other fuels the spontaneous ignition temperatures in common cases are: The additives are usually claimed to give less carbon and soot deposits in furnaces and less gum and general deposits in I. It is unwise to ballast oil fuel tanks with salt water as this accelerates the deposit of V Oil Fuel Additives Fused slag products.

Flame temperature. UPPER 4. A particular type of additive gives the following reactions: For sulphur dioxide: There is an increase in C02 content due to more complete combustion of the carbon.

Gas concentration and mixture will also have pronounced effects. Values of spontaneous ignition temperature being lower usually in oxygen and also being affected by pressure. The values quoted are theoretical calculated values as the actual values are very difficult to measure.

Pressure increase is similar but more marked with upper limit increasing and lower limit falling. Removal of Vanadium Pentoxide removes one of the catalysts that assist the formation of sulphur trioxide. For vanadium pentoxide: B then C. Various types of apparatus are available. Aspirator bottle water is mixed with sulphuric acid or made salty to stop absorption and methyl orange or other acids or alkalis are commonly used as colouring fluids see Fig.

The hot gases of exhaust containing water vapour and sulphur dioxide are quickly cooled in transit to the apparatus. Typical results: The Orsat Apparatus The enclosed volume of the apparatus is ml. The Orsat apparatus is suitable for a detailed analysis.

This causes a reduction in volume which creates a vacuum. Gaseous SOz will be registered in any hot gas analysis as C02 unless previously gas washed out by. It is suggested that for examination purposes the student should be familiar with the Orsat apparatus and any one type of COz recorder.

Water vapour condenses and sulphur dioxide is very readily absorbed by the water so that the Orsat apparatus measures COz. Pipettes must be used in sequence A. Pipette B contains a solution of potassium hydroxide and pyrogallic acid in distilled water which absorbs oxygen. This is a volumetric analysis. The reduction in Always a dry flue gas analysis i.

Pipette A contains a solution of potassium hydroxide in distilled water which absorbs carbon dioxide.

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If the gas sample were led directly to say a COz recorder by a fan so that the sample was hot then any gaseous sulphur dioxide would register as carbon dioxide unless the manganese sulphate chemical had been used to absorb the gas. Pipette C contains a solution of cuprous chloride in hydrochloric acid or ammonia.

This assumes no CO or HZ. Approximate thermal conductivities are in proportion: The wire cell resistance is proportional to heat dissipation. The sample enters via a filter and drier. Bridge electrical unbalance is dependent on C 0 2 content and the unbalance current is measured by the potentiometer. Air is used in reference cell. Thus the only difference between gas sample and air. The Boiler Combustion Heat Balance A typical analysis of the heat utilisation in an oil fired boiler would be as in Table 2.

These figures only relate to the gas or vapour by itself. H bar 0. Such fires are sometimes called 'Rusting' fires. At high temperatures the molecule bonds tend to disrupt and form molecules of the original form absorbing heat in the process. In an I. Dissociation Most combustion reactions are reversible. There is an increasing use of R numbers and gas analysis indicators. Thermal decomposition is non reversible split up under heat. C 0 bar 0. There is an increase in volume which is resisted by high pressures so as pressure rises dissociation reduces.

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Hz0 bar 0. Density of flue gas is proportional to COz content. Gas mixtures and rich oxygen contents tend to reduce dissociation considerably. Gas and air are arranged to be at equal total pressure. The torques if both in air would balance. Couple torque of impeller to vane is proportional to density of the medium in the narrow gap. Therefore the C02 content increases the density. Stainless steel components are used and bearings are of the ball race type with spring loaded adjustments. Smoke detectors are included in Chapter 8.

Emissions from a forced draught oil fired boiler furnace or an oil engine must not be longer than 10 minutes with dark smoke in the aggregate in any period of 2 hours and not more than 4 minutes continuous dark smoke except when soot blowing a water tube boiler. In a fire there is a danger that the use of superheated steam as an extinguishing agent say sootblowers on an air heater fire could in fact feed the fire and accelerate the growth.

The practical applications of smoke colour indications and combustion equipment effects are discussed later in this chapter. Once the temperature falls the molecules reform recombustion and heat is again evolved. Although the total displacement reaction is reversible the main factor is decomposition of steam vapour and dissociation of steam vapour plays a relatively minor part.

If these are dirty or the sprayer plates are damaged then atomisation of the fuel will be affected. Oil pressure is also important since it affects atomisation and lengths of spray jets. If the oil temperature is too low oil does not readily atomise since its viscosity will be high.

Ideally the mesh in the last filter should be smaller than the holes in the burner sprayer plate.

However COz content is often required to give the efficiency of combustion for a particular plant. The condition of the gases leaving the funnel is often the best indication of combustion conditions. Condition of burners. It could also produce panting which can result in structural defects. Minimum excess air and lowest practical flue gas temperature bearing in mind complete combustion and corrosion in uptakes. If the oil is dirty it can foul up the burners.

If the oil temperature is too high the burner tip becomes too hot and excessive carbon deposits can then be formed on the tip causing spray defects. Water in the oil can affect combustion. Filters are Fig. Black smoke due to insufficient air among other things.

F G temperature - Oil. To ascertain if the combustion is good. Types include pressure jet. Atomisation and combustion are greatly improved. Preheated pressurised fuel is supplied to the burner tip which produces a cone of finely divided fuel particles that mix with the air supplied around the steel burner body into the furnace.

It is impossible to remove the burner from the supporting tube unless the oil fuel is shut off. Deposits are greatly reduced.

A safety point of some importance is the oil fuel valve arrangement. The excess air supply is governed mainly by the air pressure and if this is incorrect combustion will be incorrect. Good mixing of the fuel particles with the air is essential. A small constant quantity of oil fuel in this case is passed through the fine capillary tube. This differential pressure in two tappings. The major disadvantage of this type of burner is that it uses steam-which means water and fuel-but the steam consumption in the latest type of steam atomiser is extremely small.

Maximum oil pressure is 22 bar and steam is supplied at 12 bar. As the flow is arranged t o be streamline laminar. Ultrasonic energy wave vibration. The ultrasonic atomiser bottom sketch of Fig.

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It gives high turn down ratio and low excess air. Increased differential pressure. It Viscosity Control Consider the viscometer Fig. A gear pump is driven by a constant speed electric motor through a reduction gear.

Differential pressure from the viscometer is applied across the diaphragm of the transmitter. Atomisation is excellent over a wide range of loads and the turndown ratio is as high as With improved combustion. At equilibrium both nozzles are almost closed which minimises air wastage. The output signal is fed to a controller and recorder to control the steam flow to the oil fuel heater which will cause viscosity adjustment.

The actuator has a piston and valve positioner. The Viscotherm unit works on a similar principle but there is no relay. The feedback bellows pressure is the control output signal. Movement right closes supply and opens discharge pressure decreases.

It is generally not good control practice to control one variable by means of another this induces time delays and can cause appreciable offset but it is sometimes unavoidable.

The free end of the flapper is spring loaded. The controller has desired value setting and incorporates a reset integral action. It is only proposed here to outline fuel technology aspects. These vessels have special requirements relating to construction. Guide to the Compatibility of Chemicals'. The air inlet nozzle is closed in and air pressure builds up in the feedback bellows due to a relay not shown on Fig. This detail has been simplified on Fig.

Transmitter diaphragm chambers are filled with glycerine or silicone as oil would clog the parts. Movement of the balance beam left is arranged to close discharge and open supply pressure increases. Reactions with air. Equilibrium occurs when the feedback force equals the originating force. Explosive Vapours With low flash point products the danger may exist that the atmosphere lies between the LEL and the HEL therefore creating the risk of explosion.

The Threshold Limit Value TLV gives the concentration of a substance in air in ppm which must not be exceeded if daily eight hour exposure over extended time periods is intended.

Typical TLV values are Anilene 9. Utilisation as a dual fuel requires sophisticated instrumentation on the gas side and safety interlocks between the two fuel systems. The supply gas can vary appreciably in composition during the voyage and close monitoring of composition. Carbon Disulphide. Typical flash points are Pentane. Boiling points are lower than for LNG. Benzene Combustion Equipment Vaporisation of the liquid boil off about 0.

Toxic Vapours A number of chemicals have toxic limits well below their combustible gadair concentration ratio and it is unsafe to enter spaces even if the gas concentration is below the Lower Explosive Limit LEL.

Boiling point is about. Oxygen analysers. Methanol but the value can be very low. Complexities also arise due to differing air requirements.

Heat flow through insultation causes gradual evaporation which maintains pressure above atmospheric and prevents ingress of air. Carbon Tetrachloride lo. Vapour pressure is that constant pressure during isothermal isobaric evaporation or condensation. LPG liquid petroleum gas includes such as propane. This disturbs the bridge balance and a current flows. The instrument is now charged from the suspect gas space and while operating the bulb.

Voltage is adjustable from battery B by the rheostat Switch S2is now opened. If a flammable or explosive gas is present it will cause the detector filament to increase in temperature. What is meant by the term calorific value and how does the calorific value of fuel oil compare with that of coal?

Complete the following combustion equations: Explain these two terms. The zero adjustment rheostat F can now be adjusted so that galvanometer G reads zero.

When referring to fuel oil Cetane Number and Conradson Number are often used. Why is the flash point an important criteria with regard to lubricating oil.

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On-off switch S2 is closed together with check switch S. Explain the meaning and importance of the readings obtained. Sketch the apparatus used and describe the test to determine the following properties of oil: With reference to fire or explosion explain the significance of the following properties of a flammable gas: Describe shipboard tests to determine: Class 1 1.

How the accuracy of the recorder is checked and d adjusted. Explain the effects of differences in chemical composition. Describe how engine operation and maintenance may need changing in order to burn heavy distillate instead of light distillate fuel.

For a carbon dioxide recorder explain: Define each of the following terms in relation to lubricating oil: Define the significance of lower and higher calorific value in assessing the standard of liquid fuel. Where D is the diameter of also 2 4 the seating of one valve, in mm. They may both be in the same valve chest, which must be separate from any other valve chest.

The chest may be connected to the boiler with only one connecting neck. The safety valves must never be less than 38 mm in diameter and the area of the valves can be calculated from the following formula: C i s a discharge coefficient whose value depends upon the type of valve.

If we consider a boiler operating under fixed conditions of discharge rate i. H x E , pressure P then, from Hence if C is increased, D must be reduced.

But if D is reduced the lift of the valve must be increased in order to avoid any accumulation of pressure. This is accomplished by improving the type of valve fitted to the boiler. D2and D3 are the diameters of the seating of the valves in mm. Improved High Lift Type For low pressure water tube boilers and fire tube boilers of the Scotch and other varieties, the safety valve generally employed is Cockburns improved high lift type. The operative parts of this valve are shown in Fig.

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This valve has generally superseded the ordinary and high lift types of safety valve. The essential differences between these three safety valves are as given in Table 3. The action can be seen in Fig. For superheated steam the aggregate area through the seating of the valves is increased, the formula is: Valve seat sec. Hence the improvements to the high lift safety valve are 1 Removal of valve wings, this improves waste steam flow and reduces risk of seizure 2 Floating ring or cylinder which reduces risk of seizure.

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The three spring loaded safety valves, ordinary, high lift and improved high lift, all make use of a special shaped valve seat. A, is obviously greater than A , the reason being that the specific volume of the steam has increased with the increase of temperature at constant pressure and more escape area is required to avoid accumulation of pressure specific volume is volume per unit mass.

The area of the valve chest connecting neck to the boiler must be at least equal in cross sectional area to one half of the aggregate area A , determined from equation 1. The waste steam pipe and steam passage from the valves must have a cross sectional area of at least:. A drain pipe must be fitted to the lowest part of the valve chest on the discharge side of the valves and this pipe should be led clear of the boiler.

The pipe must have no valve or cock fitted throughout its length. This open drain is important and should be regularly checked, for if it became choked, there is a possibility of overloading the valves due to hydraulic head, or damage resulting due to water hammer.

Materials Materials used for the valves, valve seats, spindles, compression screws and bushes must be non-corrodible metal, since corrosion of any of these components could result in the valve not operating correctly. Often the materials used are: Bronze, stainless steel or monel metal, depending upon conditions. The valve chest is normally made of cast steel.

Maintenance and Adjustment The makers figures relating to lip clearances, seating widths and wing clearances, etc. All working parts should be sound, in alignment and able to function correctly. When overhauling safety valves, care must be taken to ensure the parts are put back in their correct order. When dismantled, the parts are hung by a cord and sounded by gently tapping with a hammer.

If they do not ring true, examine for faults. Check drains and easing gear. Adjustment or setting of safety valves of the direct spring loaded type: With compression rings removed, screw down compression screws, raise boiler pressure to the required blow off pressure. Screw back compression screw until valve blows, then screw down the compression screw carefully, tapping the valve spindle downwards very lightly whilst doing so, until the valve returns to its seat and remains closed.

When set, split compression rings have to be fitted, then hoods, keys, padlocks and easing gear. Finally check and operate easing gear to ensure it is in good working order. For a multi-boilered installation, raise all the boiler pressures to the required blow off pressure, make sure the boilers are connected up, then proceed as described above, setting each valve in turn.

Accumulation of Pressure Test Classification societies require that when initially fitted to boilers safety valves must be subjected to an accumulation of pressure test to ensure the valves are of the correct discharge capacity for the boiler. To conduct such a test, all feed inlets and steam outlets to and from the boiler respectively, must be closed, and maximum firing rate arranged.

Accumulation of pressure must then not exceed 10 per cent of the working pressure. Duration of test water permitting is not to exceed 15 minutes for cylindrical boilers and 7 minutes for water tube boilers. In the case of water tube boilers the test may be waived if damage to superheaters or economisers could result from the test. Details of spring, compression nut, easing gear and valve chest etc. The operation of the valve is as follows: When the valve has lifted a small amount the escaping steam pressure can then act upon the full area of the valve, this increases the lift until the lower edge of the valve just enters the guide.

At this point the reaction pressure generated by the escaping steam with the guide causes the valve to lift further until it is fully open. When the valve is fully open the escape area is said to be equal to the area of supply through the seating.

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This type of valve is suitable for high pressure boilers, since the greater the boiler pressure the more rapid will the valve close, and hence the greater the saving in steam.

The main valve spring assists closing of the valve and also ensures that the valve will be closed when the boiler is cold. Upcoming SlideShare. Like this presentation? Why not share! An annual anal Embed Size px.

Start on. Show related SlideShares at end. WordPress Shortcode. Published in: Full Name Comment goes here. Are you sure you want to Yes No. No Downloads. Views Total views. The most popular and most convenient form of fusion welding is the electric arc welding process. Welding processes which do not require any pressure are often referred to as fusion welding processes.

Examples of resistance welding are: Fusion welding processes require a filler metal and often a flux is used. Electric Arc Welding In this process an electric arc is struck between the electrode. The heat which is generated inorder to form the weld depends upon 1 the square of the current supplied 2 the metal to be welded and the contact resistance 3 the time of application of current and pressure. Resistance welding is another forge welding process.

The heat which is generated causes the electrode to melt and the molten metal is transferred from the electrode to the plate Fig. If the electrode is bare. Less plant maintenance required. Also when welding is interrupted for changing of electrode or when another run is to be laid. The arc and molten metal are completely surrounded by argon gas which is supplied to the torch under pressure.

Also due to the larger contraction of the slag than the metal as cooling is taking place. Electric arc welding may be done using d. It could be caused by incorrect current or voltage. The defects are generally due to mal-operation of the welding equipment and for this reason welders should be tested regularly and their welding examined for defects.

This is a large cavity caused by entrapped gas.. A group of small gas pockets. Other forms of electric arc welding include the argon arc process. Initial cost is less for similar capacity plants.

Most of the surface defects that occur in welding can be removed by grinding but internal defects. Globules or particles of metal scattered on or around the weld. Disadvantages of a. The coating also shields the arc and the molten metal pool from the atmosphere by means of the inert gases given off as it vaporises.

During welding by the metal arc process some of the points to be observed are: Argon arc welding enables non-ferrous metals such as aluminium. More compact plant. Is a gap caused by failure of the weld metal to fill the root. By completely excluding the atmosphere during welding the argon gas prevents oxidation products and nitrides being. Argon is one of the rarer inert atmospheric gases obtained from the atmosphere by liquefaction. During welding the slag must not be allowed to get in front of the molten metal or it may become entrapped.

About 50 open circuit volts are required to strike the arc when d. Inspection of welding should be carried out during welding. Some of the defects with causes are: This is caused by an overflow. In this welding process called the T.

This may be due to a fast welding speed or too low a current. This could occur between weld metal and parent metal. Higher efficiency than d. Tungsten inert gas the arc is struck between a non-consumable tungsten electrode and the parent metal. This may be caused by too high a current 1 2 3 4 or voltage making the metal splash or splatter.

This gives better stability. This is a groove or channel along the toe of the weld caused by wastage of the parent metal which could be due to too high a welding current or low welding speed. Any slag or other entrapped matter is an inclusion defect. The defect can usually be detected by a magnetic crack detector.

Surface to be welded must be free from foreign matter. To avoid these defects. The flux coating melts at a higher temperature than the electrode metal core thus the coating protrudes beyond the core during welding. Modern torches are often of the combined type. Oxy-acetylene welding can be used for welding ferrous and non-ferrous metals. Do wnhand welding A preferable terminology is 'flat position welding'. It is also a process that can be used for hard surfacing of materials such as stelliting.

Heat Affected Zone In welding or brazing it is that part of the base metal which has had its microstructure and mechanical properties altered but it has not been melted. For oxy-acetylene welding. It should be noted that the iron or steel is itself not melted but is oxidised or burnt.

The cutting oxygen oxidises the iron to a magnetic oxide of iron Fe which has a low melting point. Once the ignition point is reached the cutting process is rapid. A flame cutting torch is different to a welding torch in that it has a separate.

Brazing and Soldering processes are similar in that the filler metal must 1 wet the parent metal 2 be drawn into the joint by capillary action. Brazing filler metals are alloys of copper. A flux is used to dissolve or remove oxides. Flame cutting or burning as it is sometimes called is convenient.

When cutting. Then the cutting oxygen is supplied and immediately burning commences. Due to the rapid cooling of the plate edge. Explain the difference between "strength" and "stiffness" of steel. Would you expect a similar diagram if you tested a non-ferrous metal?

Briefly describe the tests made on a piece of metal to determine its suitability for use in engineering. Class 2 1. What is the advantage of case hardening. Sketch graphically. C Safety factor. C Manganese. What is meant by the following terms: State the approximate proportions of carbon contained in a Cast Iron and b Cast Steel and mention the forms in which the carbon may occur therein.

Explain the essential differences between the properties of cast iron and mild steel. Compare the physical properties of these two metals and name some of the more important parts of machinery for which these materials are respectively suitable. Explain clearly what is meant by any four of the following metallurgical terms: Discuss the importance of these properties in shipboard structural members and machinery components.

Describe the effects of varying the percentages of the following constituents on the physical properties of steel: Describe the following: Explain why a material may fracture when stressed below its yield point. Asphalt is mainly found in residual oils and is an indefinite substance. Name four copper alloys associated with Marine Engineering. Primary separation. The bulk of the crude is taken to the refinery for processing into a wide range of products depending on the type of crude.

The type obtained depends on the source and also determines the type of refining necessary and nature of the end products produced. Give examples of components which might fracture in this way if suitable precautions are not taken. In each case give two examples of the metals in use on board ship. Give the approximate composition. Composition of Petroleum Consists in all its forms of hydrocarbons. The raw petroleum at the well head is often associated with natural gas.

Give properties. Explain how such fractures can be avoided with reference to the materials chosen. The lowest members of any series are gases. This depends on the lightness of the various fractions and their distillation temperatures. With slight deviations from the molecular grouping system millions of different combinations called isomers are possible. A typical primary distillation would be approximately as shown in Fig.

C Hz for example. Considering for example the paraffin hydrocarbon series: H n 2 for example. The Distillation Process As a first stage the refinery distills the crude petroleum into basic products. CnH n. Types of hydrocarbon are made up of at least nine recognisable series. Unsaturated series are rarely found in the crude petroleum but tend to be found by molecular bonding alteration during later processing. Composition and characteristics then tend to become chemically complex.

Any refinery must be fairly flexible to cope with reasonable variations of crude type and variation in market demands for the output of distillates. The actual layout is slightly more complex due to recirculation for stripping. The crude is fractioned into the various distillates by heating in fractioning towers. Further Processing To improve the quality of the distillates for use in specialised equipment. Kinematic viscosity is the ratio of the absolute viscosity to the density at the temperature of viscosity measurement.

Density is taken by hydrometer. The cracking point occurs when dissociation from heavy hydrocarbon molecules to lighter forms takes place.

Lubricating oils are produced by vacuum distillation. The object in certain specialised cases is improvement in Diesel Ignition Quality. This may be by thermal high pressure or temperature or catalytic means.

This is important for bunker capacities. These are complex processes such as thermal and catalytic cracking. Olefins and aromatics of widely varying chemical bonding are produced May be defined as the resistance of fluids to change of shape. The provision of the vacuum stage is to reduce the required temperatures of distillation for the heavier fractions to avoid oil cracking. Absolute dynamic viscosity as used in calculation is difficult to determine. It is essential to specify the temperature at which the viscosity is quoted otherwise the value becomes meaningless for correlation.

International standardisation has encouraged the development of the kinematic method. The result is expressed as time in seconds at the quoted temperature. It is expressed as the number of seconds for the outflow of a fixed quantity of fluid through a specifically calibrated instrument at a specified temperature.

Kinematic methods are increasingly being used. Redwood No. In American practice the Saybolt Universal and Saybolt Furol were used in a similar manner to the above. In European practice the Engler viscometer was used. For practical purposes viscosity is still often measured on a time basis.

Samples and apparatus require to be clean and the appliance must be level. Viscosity Scales In British practice the Redwood yiscometer was used. The time for 50 ml outflow is taken by stopwatch. Kinematic viscosity is measured by capillary flow of a set liquid volume from a fixed head Poiseuille. Temperature and viscosity are closely related in the choice of an oil for a particular duty.. Temperature accuracy is vital and a variation of k O. Considering Fig. For atomisation of fuels it is necessary to heat high viscosity oils so that the viscosity is about 30 cSt at the injector and preferably near 13 cSt for internal combustion engines the viscosity of Diesel oil being about 7 cSt at 38'C.

Some aspects relating to oils and the use of closed flashpoint may be considered as follows: The test may be open or closed depending on whether the apparatus is sealed or not. Just before the flashpoint is reached a blue halo occurs around the flame. Approximate closed flashpoint values for different oils are: From Fig. Referring to Fig. The value of viscosity index is usually determined from a chart based on a knowledge of the viscosity values at different temperatures.

It is not possible to calculate viscosities at different temperatures without the use of viscosity-temperature curves. The closed flashpoint is always lower because the lid seal allows accumulation of the volatiles above the liquid surface.

The test applied for oils above 45"C. Diesel and fuel oils. A fresh sample must be used for every test and care must be taken that no trace of cleaning solvents are present in the oil cup. Factors influenced by viscosity may be summarised as: Each oil and blend type differs with the effect of temperature change so a curve requires to be plotted for each type.

Viscosity Index is a numerical value which measures the ability of the oil to resist viscosity change when the temperature changes. The flame element is depressed through one port above the oil surface. A high viscosity index would refer to an oil capable of maintaining a fairly constant viscocity value in spite of wide variation in the temperature.

When the operating handle is depressed the shutter uncovers the ports down movement of the handle opens a shutter just below the ports by means of a ratchet. The test as conducted is very closely detailed and only a brief synopsis is outlined here. For further close details. The oxygen supply is to give an internal pressure of 26 bar and should not be less than 24 times the theoretical oxygen required.

The thermometer used can be read by means of a lens to 0. In special cases where high viscosity oils are used and high degrees of heating are required to produce atomisation.

As flashpoint is indicative of the fire and explosion risk. The interior of the bomb must be resistant to condensed acidic vapours from combustion. There are numerous makes of bomb calorimeters but the differences are only slight. Approximate heat energy values of fuels are: For shipboard requirements it is a rule that the oil for propulsion The value quoted is the higher calorific value in every case in preference to the lower value.

Fuels always exhibit a fall of calorific value to some extent during storage. The lower calorific value is more realistic. Great care should always be taken regarding the control of heat to heaters situated on the suction side of the fuels pumps so as not to cause oil vaporisation and the possibility of explosive vapour formation.

The higher calorific value includes the heat in water vapour formed from water as the products of combustion are cooled. Consider Fig.

The water equivalent W. A small specimen is fired by electric charge under conditions of pressurised oxygen and the temperature rise of apparatus and coolant is noted. This value is an important consideration for lubricating oils working under low temperature conditions e. Correction factors are now applied for acids formed under bomb conditions only. This is the calorific value reference fuel.

The above calculation. Various mixtures are used in the bath. It should be noted that under the bomb's combustion conditions high excess air and pressure sulphuric and nitric acids are formed. After removal of sample and weighing.

The result being expressed as say 1 Q7o Water. The covers must be a loose fit to allow vapours to escape. The actual apparatus must be constructed to specific and graduated::? The following test is more suitable for oil: The mass of the sample placed in the silica crucible must not exceed 0. The test is usually repeated a number of times to obtain a uniformity of results. This test has been used much more in recent times in line with the use of high viscosity fuels in Z.

The heating and test method are closely controlled. Water vapours are carried over with the distilled gasoline and are condensed in the condenser and measured in the lower part of the receiver.

The test usually conducted is the Z. This sketch is very much simplified. Steady heat is applied for about one hour. The test is a means of determining the residual carbon. Speed and cetane number can be correlated. Test Iso-octane Ca H16 has very good anti knock properties and is taken as upper limit Also the time interval between fuel injection and firing. These are more complex laboratory tests whose description is difficult to simplify and therefore are not considered further.

The oil is often alkaline. This number is the mass. In this case tetraethyl lead T. Three other tests however. Alternatively the quantities can be expressed in ppm for 1 ml of oil sample usually dissolved in industrial methylated spirits.

The test is conducted under fixed conditions on a standard engine which usually has electronic detonation detection. The test must also be carried out under closely controlled conditions. In a compression ignition engine. Knocking or pinking are characteristic of some I. In view of this these tests namely.. Ash consists usually of hard abrasive mineral particles such as quartz.

H16 has very poor anti knock properties and is taken as lower limit zero. The ash is then expressed as a mass percentage of the original sample. Phenolphthalein can be used as the indicator. Normal heptane C. Therefore octane number is the percentage by volume of iso-octane in a mixture of iso-octane and normal heptane which has the same knock characteristics as the chosen fuel.

Paraffin hydrocarbons have the best ignition quality and are thus most suitable. Modern fuels. This means that by the time the last gas charge is reached the flame front speeds can reach 2. Test Cetane is a paraffin hydrocarbon. The lubricating oil sample is mixed with water and heated. Density is often indicative of cetane number especially in the middle ranges. Thus cetane number is numerically the percentage by volume of cetane in a mixture of cetane and alpha-methyl-napthalene that matches the chosen fuel in ignition quality.

There are a number of tests. Some success has been achieved by the use of additives such as acetone peroxide. This would indicate extra heating. These combustibles when supplied with oxygen 0 2 from atmospheric air combust and liberate heat.

This chemical process liberates about Exothermic reactions are those involving heat evolution. H Z and sulphur 3. By condensation of these vapours and separation. If the carbon is incompletely burned to form carbon monoxide C O and that gas leaves the system unburned the following results.

As a generalisation the 'heavier' the oil the higher the viscosity and flashpoint and the lower the calorific value. It is also important to check the lubricating oil for water contamination. Severe corrosion of crankshafts has been caused by sulphur products from fuel oil mixing with any water in the lubricating oil to form sulphuric acids which are carried round the lubricating oil system.

Alpha-methyl-napthalene is of low ignition quality and is taken as the lower limit of zero. Analysis of Fuel Oils Typical It is not practice to assume a trend with one variable will apply to another. An alternative method called Diesel index can be used but it is not as reliable as cetane number. This chemical process liberates about 9. The percentage of SO3 to SO2 during normal combustion is low.

This reaction is of negligible importance from a heating viewpoint but is very important from the viewpoint of corrosion. Icv hydrogen The residual oils in regular use today contain. At high temperatures the very small percentage of the sulphur present as sulphates in the fuel is partly expelled as sulphur trioxide SO3. W el m hcv hydrogen If the steam escapes from the plant uncondensed. The 2. A series of common gases and their properties in combustion are given in Table 2. Nitrogen takes no part in the combustion process merely representing a large but unavoidable heat loss as being inert it is heated and passes up the uptakes to waste.

Value varies from In practice complete combustion can only be achieved by supplying excess air. Chemical reaction: This results in the condensation of acid vapours on colder metal surfaces.

Sulphurous acid is relatively harmless and unstable and in the presence of free oxygen. Methane is a gas released in bunker spaces. Other hydrocarbons. Olo C 0 2 by mass is higher. Standard temperature and pressure stp is usually adopted as a basis in combustion work. The terms stp and ntp are not rigid in definition and the assumptions made should be clearly stated. Dilute acids attack the metal continuously but strong acids cause an initial attack which is then stifled by a passive gas layer or skin developed on the metal surface.

All the combustion equations given are based on perfect gases measured at the same temperature and pressure. The oxygen required for combustion on a theoretical basis can be determined from the combustion equations.

CH4 at All the figures given in Table 2. In the I. This is a very relevant problem in air heaters and economisers of boiler plant and cylinder liners of I. Temperature increase tends to increase the range of flammability.

The presence of SO3 has been shown to raise the acid dewpoint of the gases. For really elevated boiler conditions Calcium Hydroxide or Zinc Oxide additives can be used: The sulphate compounds formed have a higher ash melting point and there is little risk of fused deposits. LOWER 4. The values quoted are theoretical calculated values as the actual values are very difficult to measure.

In the case of other fuels the spontaneous ignition temperatures in common cases are: Gas concentration and mixture will also have pronounced effects. A particular type of additive gives the following reactions: For sulphur dioxide: It is also usual to find an increase in flue gas temperature indicating better furnace or cylinder combustion. Theoretical values are based on cold gas with theoretical cold air supplied.

Flame temperature. Removal of Vanadium Pentoxide removes one of the catalysts that assist the formation of sulphur trioxide. It is unwise to ballast oil fuel tanks with salt water as this accelerates the deposit of V Additives are usually added directly to the empty oil fuel bunker tank before bunkering in quantity about 0.

Na2S04and FezS04 as the salt water compounds act as a flux as well as providing slag products directly. Pressure increase is similar but more marked with upper limit increasing and lower limit falling.. Values of spontaneous ignition temperature being lower usually in oxygen and also being affected by pressure.

For vanadium pentoxide: The additives are usually claimed to give less carbon and soot deposits in furnaces and less gum and general deposits in I.

Oil Fuel Additives Fused slag products. UPPER Pipette A contains a solution of potassium hydroxide in distilled water which absorbs carbon dioxide.

If the gas sample were led directly to say a COz recorder by a fan so that the sample was hot then any gaseous sulphur dioxide would register as carbon dioxide unless the manganese sulphate chemical had been used to absorb the gas. Pipette C contains a solution of cuprous chloride in hydrochloric acid or ammonia. This causes a reduction in volume which creates a vacuum. Water vapour condenses and sulphur dioxide is very readily absorbed by the water so that the Orsat apparatus measures COz.

B then C. Pipettes must be used in sequence A. The Orsat apparatus is suitable for a detailed analysis. By using the aspirator. Pipette B contains a solution of potassium hydroxide and pyrogallic acid in distilled water which absorbs oxygen. The reduction in. Aspirator bottle water is mixed with sulphuric acid or made salty to stop absorption and methyl orange or other acids or alkalis are commonly used as colouring fluids see Fig.

It is suggested that for examination purposes the student should be familiar with the Orsat apparatus and any one type of COz recorder. The hot gases of exhaust containing water vapour and sulphur dioxide are quickly cooled in transit to the apparatus. This is a volumetric analysis.

Gaseous SOz will be registered in any hot gas analysis as C02 unless previously gas washed out by. The Orsat Apparatus The enclosed volume of the apparatus is ml.

Typical results: Air is used in reference cell. Thus the only difference between gas sample and air. Bridge electrical unbalance is dependent on C 0 2 content and the unbalance current is measured by the potentiometer. The wire cell resistance is proportional to heat dissipation. This assumes no CO or HZ.

Approximate thermal conductivities are in proportion: Clean Air Act It is an offence to discharge smoke into the atmosphere. At high temperatures the molecule bonds tend to disrupt and form molecules of the original form absorbing heat in the process. The Boiler Combustion Heat Balance A typical analysis of the heat utilisation in an oil fired boiler would be as in Table 2.

There is an increasing use of R numbers and gas analysis indicators. C 0 bar 0. Emissions from a forced draught oil fired boiler furnace or an oil engine must not be longer than 10 minutes with dark smoke in the aggregate in any period of 2 hours and not more than 4 minutes continuous dark smoke except when soot blowing a water tube boiler.

Once the temperature falls the molecules reform recombustion and heat is again evolved. Thermal decomposition is non reversible split up under heat. H bar 0. Stainless steel components are used and bearings are of the ball race type with spring loaded adjustments. Although the total displacement reaction is reversible the main factor is decomposition of steam vapour and dissociation of steam vapour plays a relatively minor part.

Hz0 bar 0. Such fires are sometimes called 'Rusting' fires. Therefore the C02 content increases the density. Dissociation Most combustion reactions are reversible. The torques if both in air would balance. Gas mixtures and rich oxygen contents tend to reduce dissociation considerably.

These figures only relate to the gas or vapour by itself. In an I. The practical applications of smoke colour indications and combustion equipment effects are discussed later in this chapter. Smoke detectors are included in Chapter 8. Gas and air are arranged to be at equal total pressure. In a fire there is a danger that the use of superheated steam as an extinguishing agent say sootblowers on an air heater fire could in fact feed the fire and accelerate the growth.